JP-A-2002-306976 discloses a method that includes mixing an oil-soluble monomer that does not include an ion-exchange group, a surfactant, water, and an optional initiator to obtain a water-in-oil emulsion, and polymerizing the water-in-oil emulsion to obtain a monolithic organic porous body having a continuous macropore structure. A monolithic organic porous body obtained by the above method and an organic porous ion exchanger obtained by introducing an ion-exchange group into the monolithic organic porous body may be useful as an adsorbent, a chromatography packing material, and an ion exchanger used for a water deionizing apparatus or the like.
However, when increasing the ion-exchange capacity per unit volume of the organic porous ion exchanger in water-wet conditions by reducing the total pore volume, the size of the mesopores (openings) significantly decreases. The openings disappear when further reducing the total pore volume. Specifically, the ion-exchange capacity per unit volume decreases when achieving a low pressure loss required for practical applications, and the pressure loss increases when increasing the ion-exchange capacity per unit volume.
Moreover, the area of the skeleton observed within the section of the monolithic organic porous body or the organic porous ion exchanger obtained by the above method is theoretically limited to less than 25%. This is because the monolithic organic porous body having a continuous macropore structure (i.e., an intermediate body of the organic porous ion exchanger shown below is produced using a water-in-oil emulsion. It is necessary to cause the water droplets contained in the water-in-oil emulsion to come in contact with each other in order to form a continuous macropore structure. Therefore, the volume fraction of the water droplets is limited to 75% or more. Since a monolithic organic porous body obtained by stationary polymerization of the water-in-oil emulsion has a configuration in which the structure of the emulsion is immobilized, the porosity of the monolithic organic porous body is 75% or more. Accordingly, the open frontal area of the section of the organic porous body is also 75% or more (i.e., the area of the skeleton observed in the section is less than 25%). Therefore, the area of the skeleton observed in the section cannot be increased when using the above method.
For example, JP-T-7-501140 discloses a porous body having a particle aggregation-type structure as a monolithic organic porous body or a monolithic organic porous ion exchanger having a structure other than the continuous macropore structure. However, since the continuous hole of the porous body obtained by the method disclosed in JP-T-7-501140 is small (about 2 μm or less), the porous body cannot be used for an industrial deionized water production apparatus or the like that treats the target water at a high flow rate under low pressure. Moreover, a porous body having a particle aggregation-type structure has low mechanical strength, and may break when cut to a desired size and placed in a column or a cell (i.e., exhibits poor handling capability).
Therefore, development of a monolithic organic porous ion exchanger that is chemically stable, has high mechanical strength and a large ion-exchange capacity per unit volume, and ensures a low pressure loss when fluid (e.g., water or gas) passes through due to a large continuous hole, has been desired.
An organic porous body having a co-continuous structure that includes a three-dimensional continuous skeleton phase and a three-dimensional continuous hole phase defined by the skeleton phase has been known. JP-A-2007-154083 discloses an organic polymer gel affinity support having a co-continuous structure that includes a three-dimensional continuous pore having an average diameter in the order of micrometer, and a skeleton phase that is mainly formed of an organic material, the affinity support being a copolymer of at least one of a di- or higher functional vinyl monomer compound, methacrylate compound, and acrylate compound (crosslinking agent) and a monofunctional hydrophilic monomer, the volume ratio of the crosslinking agent and the monofunctional hydrophilic monomer in the affinity support being 100 to 10:0 to 90. The crosslink density of the skeleton of the affinity support is increased in order to maintain the monolithic structure. The affinity support has hydrophilicity that sufficiently suppresses nonspecific adsorption. N. Tsujioka et al., Macromolecules 2005, 38, 9901 discloses a monolithic organic porous body that has a co-continuous structure and is formed of an epoxy resin.
Since the pore of the affinity support disclosed in JP-A-2007-154083 has an average diameter in the order of micrometer, the pressure loss when fluid passes through the affinity support increases. Therefore, it is difficult to use the affinity support as an ion exchanger for a water deionizing apparatus that treats water at a high flow rate under low pressure loss. Moreover, since the affinity support is hydrophilic, a complex and expensive operation (e.g., surface hydrophobic treatment) is required to use the affinity support as an adsorbent for a hydrophobic substance. Moreover, it is difficult to introduce a functional group (e.g., ion-exchange group) into an epoxy resin.
Therefore, development of a monolithic organic porous body that is chemically stable and is hydrophobic, has high hole continuity and uniformity, and ensures a low pressure loss when fluid (e.g., water or gas) passes through the monolithic organic porous body due to a large continuous hole, has been desired. Development of an monolithic organic porous ion exchanger that has a large ion-exchange capacity per unit volume in addition to the above properties has also been desired.
An MR ion-exchange resin has a composite particle structure that includes a copolymer having a large network structure in which micropores formed between macropores and small spherical gel particle aggregates. However, the diameter of the particles that form the micropores of the MR ion-exchange resin is 1 μm or less, and a composite organic monolithic body in which particles or protrusions having a diameter of more than 1 μm adhere to the surface thereof has not been proposed.    (Patent Document 1) JP-A-2002-306976 (claim 1 and paragraph 0017)    (Patent Document 2) JP-T-7-501140    (Patent Document 3) JP-A-2004-321930 (claim 1)    (Patent Document 4) JP-A-2007-154083 (claim 1)